tox: Keeping going with docs

Sphinx 1.8 introduced [1] the '--keep-going' argument which, as its name
suggests, keeps the build running when it encounters non-fatal errors.
This is exceptionally useful in avoiding a continuous edit-build loop
when undertaking large doc reworks where multiple errors may be
introduced.

[1] https://github.com/sphinx-doc/sphinx/commit/e3483e9b045

Change-Id: I91ed3b79467683cfca34ef7d79afeb3e6d966f86

doc/requirements.txt

@@ -4,8 +4,8 @@
 
 # For generating sphinx documentation
 openstackdocstheme>=1.18.1 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7' # BSD
-sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4' # BSD
+sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD
+sphinx>=1.8.0,!=2.1.0;python_version>='3.4' # BSD
 reno>=2.5.0 # Apache-2.0
 sphinxcontrib-apidoc>=0.2.0  # BSD
 

tox.ini

@@ -43,7 +43,7 @@ deps =
   -r{toxinidir}/doc/requirements.txt
 commands =
   rm -fr doc/build
-  sphinx-build -b html doc/source doc/build/html
+  sphinx-build --keep-going -b html doc/source doc/build/html
 
 [testenv:cover]
 basepython = python3
@@ -66,9 +66,12 @@ import_exceptions =
 
 [testenv:releasenotes]
 basepython = python3
+whitelist_externals =
+  rm
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
-  sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+  rm -rf releasenotes/build
+  sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]
 basepython = python3